Traffic on a major Montreal highway damaged by a concrete tunnel collapse on the weekend was gradually restored Monday, as authorities tried to reassure drivers about the road's overall safety.

Vehicles were allowed back on the Ville-Marie expressway eastbound just 24 hours after a 25-tonne concrete beam crashed to the ground in the highway's tunnel.

The collapse happened in a section of the 720 tunnel near Hôtel-de-Ville Street at 9 a.m. ET Sunday. No vehicles were on the road at the time.

The Ville Marie was closed in both directions immediately after the collapse, with westbound lanes reopening late Sunday.

Authorities allowed eastbound traffic as far as the St.Laurent-Berri exit Monday morning, after some of the rubble from the collapse was removed overnight.

Transport Quebec inspectors are examining the debris and structure, while the agency stressed the overall safety of Montreal's highway network.

"We want to understand what happened for this beam to have fallen down. No theory will be dismissed, as long as we don't have an explanation," said Transport Quebec spokeswoman Caroline Larose.

The agency stressed the overall safety of Montreal's highway network, with Larose declaring she had no concerns about driving in the tunnel.

"The structure has been inspected, it's been inspected fully, completely," she said.

The concrete beam that collapsed served as a sun barrier for drivers entering the tunnel.

Work crews were repairing the tunnel's interior walls when the collapse occurred, and were the first to alert authorities.

Transport officials later noticed another unsteady concrete beam in the tunnel and used a crane to rip it down.

A spokeswoman for the provincial Transport Department says workers are now trying to stabilize a third beam.

Collapse unnerves drivers

Transport Quebec said it was too early to draw any link between wall repairs and the collapse.

The agency is expected to hand over an incident report to Quebec police, who were ordered by provincial Transport Minister Sam Hamad to investigate the accident. Hamad visited the collapse site Sunday afternoon.

'I'm really disturbed about it. I think it's an extremely serious situation.'—Kirk Bennett, Montreal driver

"Our goal is to reconstitute a timeline since 9 a.m. Sunday morning. Our investigators are there, and our collision experts are there to ensure this incident wasn't intentionally caused," said Sûreté du Québec spokeswoman Geneviève Bruno.

The collapse unnerved drivers in the area who use the expressway regularly.

"I'm really disturbed about it," said Kirk Bennett, recalling how he drove through the collapsed tunnel with his family on Friday. "I think it's an extremely serious situation."

The city announced parking bans and suggested detours for drivers wanting to use the highway.

More than 100,000 vehicles use the Ville-Marie Expressway every day. Graham Hughes/Canadian PressSouthside parking on Ontario and Saint-Antoine Streets and René-Lévesque Boulevard is forbidden starting Monday, to open up another lane for detour traffic from the Ville Marie.

Some 100,000 vehicles use the Ville-Marie expressway every day.

The Montreal area's aging road network has forced lane closures on several overpasses and bridges this summer as engineers scramble to deal with the city's crumbling infrastructure.

The Ville-Marie collapse echoed another Montreal-area highway disaster five years ago that killed five people and injured many more.

The Concorde overpass collapse sparked a frenzied public debate about Quebec's crumbling road infrastructure.

A provincial inquiry that investigated the Concorde collapse documented a pattern of poor maintenance and lax inspection protocol over decades.

The tunnel collapsed in a downtown section of the Ville-Marie Expressway. CBC